I have a '97 F250 with a MAF sensor equipped 460. I have a P0174 system too lean (bank 2) code that keeps coming up. A little history, I recently bought the truck on the cheap because it had low compression in cylinder #5. The engine had supposedly been rebuilt 20k miles previously, I pulled the engine, replaced the damaged piston, re-ringed and bearinged the engine and put it back in. It runs great, no misfires, no strange noises. I don't know if the lean condition was pre-existing or if it is new.
I hooked up the scanner, and here is the pertinent data at idle:
Long term fuel trim, bank 1: 25%
Long term fuel trim, bank 2: 19%
Barometric pressure: 78 kPa
DPFE sensor voltage: .991 V
IAC duty cycle: 59%
Intake air temp: 31 C
MAF voltage: 1.031 V
O2B1S1 voltage: varies between .1 and .9 volts, and is very active
O2B2S1 voltage: same
Engine RPM: 777
Engine coolant temp: 88 C

The only data that seems out of whack (besides the LT fuel trim) is the barometric pressure. As far as I know, there is no actual barometric pressure sensor, the value is calculated from MAF readings at full throttle. The truck is reporting 78 kPa, which according to my math, the truck thinks it is at around 7000' altitude. The truck is actually at 4300' altitude. I also have a '97 escort with a MAF sensor, I hooked the scanner up to it and it is reporting 81 kPa, which is about 6000' altidude. I would think the computer should be calculating around 88 kPa for my altitude. Is this an indication of a bad MAF?

Now, here are the things I have tried:
Checked MAF, it is clean.
Disconnected and plugged all vacuum sources on the engine, no change.
Checked intake tubes for cracks/leaks, none found.
Liberally sprayed starting fluid everywhere to detect vacuum leaks, none found.
Lower and upper intake gaskets are new.
Fuel pressure 40 psi, 46 psi with regulator vacuum hose unhooked.
Checked EGR valve, it is not leaking.
Fuel injectors are the correct F1TE-D5A, 24 lb/hr.

Right now I can see a few possibilities:
Injectors are plugged
MAF sensor is bad
There is a vacuum leak I can't find

I'm looking for suggestions, if there are none, maybe there is somebody out there who can provide me with some baseline data from their engine. I would think that if I have a vacuum leak then my IAC duty cycle would be lower than if there was no leak, and being able to compare that would be useful. I really don't want to start throwing parts at it unless I know they are bad.